10(i DESMIDS OF THE UNITED STATES. 



Genus, EUASTEUM, Ehrb. 



Cells oblong or elliptic, deeply constricted into two semi- cells 

 Tvhich are emarginate and usually incised at their ends ; sides 

 symmetrically sinuate or lobed ; provided with circular inflated 

 protuberances (rarely absent) ; viewed from the vertex, elliptic. 

 Zygospores spherical, tuberculosa or spinous. 



E. CJRASSXJ5I, (Breb.), Kg. Plate XXVIIT, figs. 1, 2, 3. 



Cells about twice as long as broad, smooth ; semi-cells three- 

 lobed ; basal lobes very broad, with a wide shallow marginal 

 sinus; terminal lobe cuneate. partly included in a notch 

 formed by the lateral lobes ; incision in terminal lobe linear 

 or acute angled. 

 Diameter 68-82 yu. 



A large, and not rare plant in shallow spring, and pond 

 waters. 



Yar. scEOBicuLATUii, Lund. Plate XXIX, figs. 4, 5. 



In outline very nearly the same as the type form, but 

 differs in having in the middle of the semi-cell four scrobi- 

 culae. Lundell represents only two ; our form has four ; 

 besides these excavations the plant has four papilla-like 

 prominences towards the ends of the semi-cells, which I do 

 not find alluded to; they may give claim for a distinct species. 

 Pond, Malaga, New Jersej'. 



E. OENATUM, Wood. Plate XXVIII, fig. 4. 



A species which is veiy close to E. crassum; perhaps not 

 separable from it. The author, Wood, says "it differs in 

 the proportionate length, being only twice instead of three 

 times as long as broad ; in the size being only three-fourths 

 as large ; and especially in the peculiar lateral splitting, as 

 it were, of the basal lobes." 



In our observations, verj' few specimens of jE. crassum ever 

 exceed two diameters in length ; they vary greatly in size, 

 and the "lateral splitting," a delusive appearance, is common 

 to all of them when the cells are empty. 



Saco Lake, New Hampshire (Wood). 



:E. oblongum, (Grev.), Ealfs. Plate XXVIII, figs. 5, 6, 7. 



Cells smooth, oblong, semi-cells somewhat five lobed; 

 lobes nearly equal, cuneate : lateral lobes, or the basal only, 

 with a broad, shallow, marginal concavity : all their angles 

 rounded ; terminal lobe partly included between the lateral 



